If the target creature is an illegal target by the time Pyrophobia tries to resolve, the spell doesn't resolve. Cowards can block if they're otherwise allowed to.
14-06-2019
wotc
Because it doesn't modify the characteristics of creatures, Pyrophobia can affect Cowards that enter the battlefield or creatures that become Cowards after the spell resolves.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.