AffinityAffinity is a static ability that functions while the spell with affinity is on the stack. “Affinity for [text]” means “This spell costs less to cast for each [text] you control.”
If a spell has multiple instances of affinity, each of them applies. (CR 702.41) for Phyrexians (This spell costs
less to
castTo cast a spell is to take it from the zone it’s in (usually the hand), put it on the stack, and pay its costs, so that it will eventually resolve and have its effect. A player may cast a spell if they have priority. See rule 601, “Casting Spells.”
To cast a card is to cast it as a spell. (CR 701.5) for each Phyrexian you control.)
FlyingFlying is an evasion ability.
A creature with flying can’t be blocked except by creatures with flying and/or reach. A creature with flying can block a creature with or without flying. (See rule 509, “Declare Blockers Step,” and rule 702.17, “Reach.”)
Multiple instances of flying on the same creature are redundant. (CR 702.9)
Phyrexian Broodstar's power and toughness are each equal to the number of Phyrexians you control.