Phantasmal Web is a 5th-level illusion spell that creates an illusory web full of spiders that torment those who believe they’re held within it, rendering them extra helpless, and has to be one of the meanest crowd-control spells, at mid-level at least.

Some choice phrases from the description:

Those who fail to disbelieve the phantasmal web are treated as if in a web spell, but must also make a Fortitude save at the beginning of each turn or become nauseated for that round by the phantasmal spiders.

Targets cannot escape the phantasmal web by moving, even by teleportation. Freedom of movement allows unobstructed movement but does not negate the concealment or nausea effects.

Targets of the spell perceive everyone else around them to be engulfed in webs and swarming spiders …

I can seriously see someone fireballing their own position to try to kill the spiders.