Jace, the Perfected Mind

Compleated ({U/P} can be paid with {U} or 2 life. If life was paid, this planeswalker enters with two fewer loyalty counters.)
[+1]: Until your next turn, up to one target creature gets -3/-0.
[−2]: Target player mills three cards. Then if a graveyard has twenty or more cards in it, you draw three cards. Otherwise, you draw a card.
[−X]: Target player mills three times X cards.

Phyrexia: All Will Be One

Compleated ({PU} can be paid with {U} or 2 life. If life was paid, this planeswalker enters with two fewer loyalty counters.)
+1: Until your next turn, up to one target creature gets -3/-0.
−2: Target player mills three cards. Then if a graveyard has twenty or more cards in it, you draw three cards. Otherwise, you draw a card.
−X: Target player mills three times X cards.

Compleated
+1: Until your next turn, up to one target creature gets -3/-0.
−2: Target player mills three cards. Then if a graveyard has twenty or more cards in it, you draw three cards. Otherwise, you draw a card.
−X: Target player mills three times X cards.

A Phyrexian mana symbol contributes 1 toward the mana value of a card, even if life is paid for it. Specifically, Jace's mana value is always 4.

Jace's second loyalty ability doesn't care which player's graveyard has twenty or more cards in it. It could be the target player's or another player's.

Other replacement effects that would change the number of loyalty counters Jace enters with will apply as normal.

The compleated ability looks only at whether a player chose to pay 2 life for a Phyrexian mana symbol as they were casting the spell. If a player paid life for some other reason while casting the spell, that will not reduce the number of loyalty counters the planeswalker enters the battlefield with.