My question is in regard to Phyrexian Altar and Omnath, Locus of Rage interaction. Does it resolve that if you use the altar to sacrifice an elemental that was generated by Omnath that you get to deal the 3 damage AND generate the mana?
If you control Omnath and Phyrexian Altar and sacrifice an Elemental you control (including an Elemental token created with Omnath) with Phyrexian Altar, Omnath's last ability will trigger. (Note that you add one mana of any color before you put that ability on the stack and choose its target [C.R. 605.3b, 603.3, 603.3d, 601.2c, 605.1a].)
You can activate Phyrexian Altar's ability as often as you can pay its cost (which is "Sacrifice a creature" here), not just once each turn (C.R. 118.3, 602.1). Compare Phyrexian Altar with Akki Avalanchers or Fault Riders, whose abilities have restrictions on how often they can be activated (C.R. 602.1b). And each time "Omnath ... or an Elemental creature you control dies" (whether by being sacrificed or otherwise), Omnath's last ability will trigger (C.R. 603.2, 700.4, 701.16a). See also this thread.
My question is in regard to Phyrexian Altar and Omnath, Locus of Rage interaction. Does it resolve that if you use the altar to sacrifice an elemental that was generated by Omnath that you get to deal the 3 damage AND generate the mana?