Does the Mordenkainen's Private Sanctum spell block summoning creatures into the warded area?

Question

If you secure an area with the Mordenkainen's private sanctum spell and choose the effect:

Planar travel is blocked within the warded area.

Does this prevent summoning creatures into the area via spells like infernal calling (XGtE, p. 158)?

Planar travel, in this instance, could either mean "willingly moving between planes" or "moving between planes under any circumstance", and I don't know which is meant by the spell.

Answer 1

The text says "Planar travel is blocked" with no other exceptions or restrictions, which means that both of your specified scenarios would be blocked, regardless of how or why it is happening. Therefore, as long as the summoning spell is summoning a creature from another plane, it would be blocked.

For example, Instant Summons would be blocked if it summoned the object from another plane, and most of the Conjure X spells would be blocked as they pull creatures from another plane.

Answer 2

Yes, the Infernal Calling spell can be blocked, as that spell specifies that "you summon a devil from the Nine Hells".

So, unless the Mordenkainen's Private Sanctum spell were cast at a location in one of the Nine Hells, Infernal Calling's effect would necessarily constitute a form of planar travel, which the Private Sanctum spell can block.

In short, if the "planar travel is blocked within the warded area" 'property' is chosen by the caster of Mordenkainen's Private Sanctum, summons from another plane will fail within that area.

The Summon Lesser Demon & Summon Greater Demon spells (which are, like Infernal Calling, from Xanathar's Guide to Everything), also specify a plane of origin (the Abyss).

In the Dungeon Master's Guide, a Ring of Djinni Summoning allows its wearer to (as an action) "summon a particular djinni from the Elemental Plane of Air." That would likewise be blocked, by the aforementioned 'property' of the Private Sanctum.

All of those summon effects are blocked by the planar travel prohibition of Private Sanctum, because they explicitly state a plane of origin that is (hopefully) not the plane on which Private Sanctum was cast.

Generally, planar travel is associated with relatively high-level spells / items / abilities. Contact Other Plane is a 5th level spell; Plane Shift is a 9th level spell. Blink is 3rd level, but sends you to the Ethereal plane only erratically, & returns you to the Material plane when it ends (1 minute duration).

All other summons & conjures from primary sources such as the Player's HandBook, state that a spirit or type of creature (or an object †) is conjured or summoned, but these spells don't state a plane from which the spirit or creature is summoned.
This includes:
• Conjure Animals (PHB)
• Conjure Celestial (PHB)
• Conjure Minor Elemental (PHB)
• Conjure Elemental (PHB)
• Conjure Fey (PHB)
• Conjure Woodland Beings (PHB)
• † Drawmij's Instant Summons (PHB)
• Summon Aberration (Tasha's Cauldron of Everything)
• Summon Beast (TCE)
• Summon Celestial (TCE)
• Summon Construct (TCE)
• Summon Elemental (TCE)
• Summon Fey (TCE)
• Summon Fiend (TCE)
• Summon Shadowspawn (TCE)
• Summon Undead (TCE)
• Summon Draconic Spirit (Fizban's Treasury of Dragons)

Depending on DM interpretation, any or all of these summons that don't define a plane of origin, might be drawn from the caster's present plane, or from another.

An actual Fey creature (as opposed to a fey spirit) is likely from the Feywild, & a conjured Celestial most likely came from a celestial plane, but those spells, like most others, don't specify a plane of origin, so in those cases it is left for each DM to decide.

Many conjure & summon spells, allow the caster to choose a location within sight (or even simply within a given range). So, the caster of Mordenkainen's Private Sanctum might also want to choose two or three of its other 'properties' for the area:
• The barrier of the warded area appears dark and foggy, preventing vision (including darkvision) through it.
• Nothing can teleport into or out of the warded area.
• Sensors created by divination spells can't appear inside the protected area or pass through the barrier at its perimeter.
These 'properties' will make it harder to summon a creature to a location just outside the Private Sanctum, from any locations inside it.

Answer 3

It depends on how one's summoning works. If your DM allows you to pull the spirits from the surrounding area and form them into creatures, then summoning could work. RAW, it prevents summoning.