Many spells have "At higher levels" that provides for more targets or more damage.
For example Magic Missile can be cast as a second level spell and shoot 4 missiles instead of it's 3 as a first level spell.
Can a spell without that verbiage, such as Firestorm be cast in higher level slots for the same effect as the lower level spell?
Yes
To cast one of these spells, you must expend a slot of the spell’s level or higher.
(Chapter 3: Classes, paragraph Preparing and Casting Spells, in the Class descriptions for both Cleric & Wizard.)
This is expanded upon in Chapter 10: Spellcasting, under Spell Slots, p78
When a character casts a spell, he or she expends a slot of that spell’s level or higher, effectively “filling” a slot with the spell. You can think of a spell slot as a groove of a certain size—small for a 1st-level slot, larger for a spell of higher level. A 1st-level spell fits into a slot of any size, but a 9th-level spell fits only in a 9th-level slot.
Only some spells specify an increased effect from using a higher slot. All others have the same effect regardless of which level slot they are cast in.
