Can Aberrant Mind Sorcerers upcast Psionic Spells using Sorcery points?

Question

Aberrant Mind Sorcerers get Psionic Sorcery at L6:

When you cast any spell of 1st level or higher from your Psionic Spells feature, you can cast it by expending a spell slot as normal or by spending a number of sorcery points equal to the spell’s level. If you cast the spell using sorcery points, it requires no verbal or somatic components, and it requires no material components, unless they are consumed by the spell.

Can you cast these spells at a higher level, using more sorcery points? I.e., cast Arms of Hadar at L2 using 2 sorcery points?

Answer 1

No.

Reading the feature more carefully and "Casting Spells at a Higher Level," it's clear that this is not possible (despite my hopes):

When a spellcaster casts a spell using a slot that is of a higher level than the spell, the spell assumes the higher level for that casting. For instance, if Umara casts magic missile using one of her 2nd-level slots, that magic missile is 2nd level. Effectively, the spell expands to fill the slot it is put into.

That is, casting at a higher level is predicated on using higher-level slots (which is not the case here). Put differently, there are 3 elements: the level of the spell (which the Psionic Sorcerer references, in singular), there is the level of the slot, and by using the higher slot, there's the level the spell assumes (i.e., that of the higher-level slot).

However, without the use of a higher-level slot, the spell can only assume its innate level. A L1 spell can only become a L3 spell by casting it with a L3 slot (but at that point, it's already cast—you can't use 3 SP to cast the L3 version).

There is no rule/allowance for up-casting with resources other than slots unless otherwise indicated (confirmed in Sage Advice):

Sage Advice Compendium version 2.3, page 13:

What level is a spell if you cast it without a spell slot?

Such a spell is cast at its lowest possible level, which is the level that appears near the top of its description. Unless you have a special ability that says otherwise, the only way to increase the level of a spell is to expend a higher-level spell slot when you cast it. (p 13)

Contrast with the Monk feature, Disciple of the Elements, discussed in the Sage Advice answer:

"The Monk’s Disciple of the Elements feature lets the monk spend ki points, rather than a spell slot, to increase the level of a spell."

Disciple of the Elements:

"Once you reach 5th level in this class, you can spend additional ki points to increase the level of an elemental discipline spell that you cast, provided that the spell has an enhanced effect at a higher level, as Burning Hands does. The spell's level increases by 1 for each additional ki point you spend."

The Psionic Sorcery feature does not mention anything like that.

More details here.

Answer 2

Yes, you can upcast spells using sorcery points.

First, Psionic Sorcery says:

When you cast any spell of 1st level or higher from your Psionic Spells feature, you can cast it by expending a spell slot as normal or by spending a number of sorcery points equal to the spell’s level.

The first notable phrase we observe is:

When you cast any spell of 1st level or higher from your Psionic Spells feature, you can...

This indicates that we first choose to cast a spell of 1st level or higher. “You can” indicates further options that we choose after we have chosen to cast a spell of 1st level or higher.

So suppose I choose to cast dissonant whispers at 3rd level. Notably, this is a 3rd level spell:

When a spellcaster casts a spell using a slot that is of a higher level than the spell, the spell assumes the higher level for that casting. For instance, if Umara casts magic missile using one of her 2nd-level slots, that magic missile is 2nd level. Effectively, the spell expands to fill the slot it is put into.

Of course, this assumes we are using spell slots to cast our spells, since this passage is taken from the general rules for spellcasting. It is only natural to talk about casting spells using spell slots in a section of general spell casting rules, since slots are generally the only way to cast spells.

Psionic Sorcery goes on to create an exception to this general rule about expending spell slots. It says:

you can cast it by expending a spell slot as normal or by spending a number of sorcery points equal to the spell’s level.

So we can cast dissonant whispers at 3rd level as normal using a spell slot, or our class feature creates an exception that allows us to use 3 sorcery points instead.

Answer 3

It's unclear

I believe the real question that needs answered here is "Are spells that are upcast considered spells of that level?" meaning is a level 2 casting of Arms of Hadar a different spell from a level 1 casting? Does different levels mean different spells?

As @Kahashir mentioned in his answer, in regards to upcasting,

Effectively, the spell expands to fill the slot it is put into.

In order to upcast a spell, you would normally need a spell slot to fill. Without a spell slot for the spell to "expand into", it will not be upcast.

However, it could also be argued that this means that the spell is uniquely different once it fills the spell slot, since it's a different level. A good argument would be Infernal Legacy (PHB 43):

Once you reach 3rd level, you can cast the hellish rebuke spell once per day as a 2nd-level spell.

Since you can ONLY cast hellish rebuke as a 2nd-level spell using this special feature, it can be argued that 2nd-level hellish rebuke is a separate spell from 1st-level.

I believe that it is up to the DM on this argument.

On the other hand...

We should also consider this answer to the question "Can you use Wish to duplicate a spell at a higher level?" with the TL;DR answer being we don't know. But the same kind of situation applies here: can the caster decide the level?

If your DM allows you to cast Wish spells at higher levels, they should probably rule that you can upcast Psionic Spells as well.