This is perhaps a trivial entry on the use of phyir but nonetheless it may be useful for some students.
§1. First of all, it should be pointed out that phyir comprises of phyi (“outside/outward”) and r (la don). Normally we would not think of separating these two components because they have, so to speak, coagulated and frozen in time.
§2. Syntactically, two uses of phyir seem particularly interesting. (a) The word phyir can be construed with verbs (mostly in a subordinate clause containing adverbial phrase of purpose and also preceding the principle clause) so to as have the meaning of “for the sake/purpose of,” “in order to/that,” “so as to.” For examples: (i) da ni ston pa phun sum tshogs pa bstan pa’i phyir | de bzhin gshegs pa yang dag par rdzogs pa’i sangs rgyas bcom ldan ’das longs spyod chen po zhes bya ba la sogs pa smos te | (RZ 1); (ii) gnas phun sum tshogs pa bstan pa’i phyir ’og min gyi gnas mtha’ dang dbus med pa na zhes smos te | (RZ 1). The syntactical structure here is: “For the sake/purpose of showing X, Y has been stated.”
§3. (b) The second and most common usage of phyir construed with a verb is in a subordinate clause containing adverbial phrase of reason, which can precede or follow a principle clause and thus having the meaning of “because.” For examples: (i) ’gro ba rnams kyi sems kyi rnang bzhin ni dbyer mi phyed pa’i phyir rdo rje’o ||; (ii) byang chub yang yin la chen po yang yin pa’i phyir byang chub chen po zhes bya’o ||; (ii) grub pa’i mtha’ thams cad kyang phyin ci ma log par mthar thug pa ni rdzogs pa chen po yin zhing de las bogs dbyung du med pa’i phyir ro ||. The syntactical structure here is something like: “Because of Z, X is Y,” or, “X is Y because of Z.”
§4. Of course, a phrase having the structure of “substantive + kyi/gyi/gi/yi/’i + phyir (with or without du)” is quite easy because it would simply mean “for the sake/benefit of X (substantive).” In this case, phyir du can be replaced by don du (with no change in meaning). Example: byang chub kyi phyir; rtsed mo’i phyir yang sems can la gnod pa byed de | (RZ 2: 386) “[People] harm sentient beings even for fun.”
§5. Also remember that we have some fixed words such as ci’i phyir (“for what sake” = “why”), gang gi phyir (“for which/whose sake,” de’i phyir (“for that sake/reason” = “thus/therefore”).
§6. It seems that phyir is also used as a kind of verbal-prefix often having the meaning of “away,” “out,” or “again.” Consider the following:
1. phyir gso ba “to revive”
2. phyir ’don pa “to ooze”
3. phyir bcos pa “to remedy”
4. phyir slog pa “to return (something to someone)”
5. phyir rgol ba “to oppose,” etc.
6. phyir bshol ba “to postpone”
7. phyir zlog pa “to repel”
8. phyir log pa “to retract”
9. phyir bkram pa “to spread out”
10. phyir dbyung ba “to expel”
11. phyir ’phul ba “to expel”
12. phyir ’bud pa “to expel”
So much for now.