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.