Phantasmal Form — ruling 1

Phantasmal Form overwrites all previous effects that set the target creatures' power and toughness to specific values. Other effects that set their power or toughness to specific values that start to apply after Phantasmal Form resolves will overwrite this effect.

Phantasmal Form — ruling 2

Effects that modify the target creatures' power or toughness (such as the effects of Force of Virtue or Giant Growth) will apply no matter when they started to take effect. The same is true for counters that change the creatures' power or toughness (such as +1/+1 counters).

Phantasmal Form — ruling 3

You may cast Phantasmal Form without choosing any target creatures. You'll just draw a card. However, if you choose any targets and all of those targets become illegal before the spell tries to resolve, the spell won't resolve and you won't draw a card.

Phantasmal Form : règles, fonctionnement et interactions (MTG)

Phantasmal Form is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Until end of turn, up to two target creatures each have base power and toughness 3/3, gain flying, and become blue Illusions in addition to their other colors and types. Draw a card.

How it works : Phantasmal Form

Original English text — Wizards of the Coast / Scryfall

#1June 14, 2019· Wizards of the Coast
Phantasmal Form overwrites all previous effects that set the target creatures' power and toughness to specific values. Other effects that set their power or toughness to specific values that start to apply after Phantasmal Form resolves will overwrite this effect.
No other card is named in this ruling.
#2June 14, 2019· Wizards of the Coast
Effects that modify the target creatures' power or toughness (such as the effects of Force of Virtue or Giant Growth) will apply no matter when they started to take effect. The same is true for counters that change the creatures' power or toughness (such as +1/+1 counters).
No other card is named in this ruling.
#3June 14, 2019· Wizards of the Coast
You may cast Phantasmal Form without choosing any target creatures. You'll just draw a card. However, if you choose any targets and all of those targets become illegal before the spell tries to resolve, the spell won't resolve and you won't draw a card.
No other card is named in this ruling.