If it got bottomless traphole or nobleman of xout, will it still come back during the standby phase?

No...because Phoenix must be in your Graveyard...

"If "Sacred Phoenix of Nephthys" is destroyed and removed from play, such as with "Bottomless Trap Hole", it is not Special Summoned from out of play during the Standby Phase, because this effect activates in the Graveyard."

what about if sacred phoenix is in the field and opponent has ocean dragon lord on the field, and then he sent umi to the grave yard which automatically sent all cards to graveyards. Does phoenix comes back during standby phase? or it isnt coz it is sent to graveyard instead of destroyed.

The only way that you can summon Sacred Phoenix after it gets removed from play is to use a card that brings it back into play, like oh..... hang on now....... AHA!! Here you go now ----- Return from the Different Dimension, Dimension Fusion, etc.

Here's something slightly worse for anybody ruuning Sacred Phoenix in their deck ---- face off against both Ocean Dragon Lord & Water Dragon out on the field, plus 2 Bonding H2O's in their hand lol.

Yes, Phoenix will NOT come back since it was not "destroyed" by a card effect, but just "sent to the Graveyard".

Ocean Dragon Lord - Neo Daedalus may not work, but Levia-Dragon - Daedalus would work.