Abilities that define a creature's power and toughness apply while that card is in exile, but abilities that add or subtract from it don't. For example, the ability of Battle Squadron applies to determine Phyrexian Ingester's power and toughness, but the ability of Werebear doesn't. Phyrexian Ingester's power and toughness are constantly updated if the exiled card's power and/or toughness change.

Phyrexian Ingester will get bonuses based on the card's power and toughness in exile. Counters, Auras, and Equipment it had on it before it was exiled won't add to those numbers.

If the card in exile isn't a creature card (perhaps because it was a land that was temporarily a creature while on the battlefield), Phyrexian Ingester doesn't get a bonus.