Creating a very sharp smartphone lock screen

Hey i work as a Graphic Designer but there is one thing i haven't made a lot of expierence with so i wanted to ask here if people know more about it.
Since Smartphones uses higher PPI values than the usual PC Monitor i wanted to create sharp Pictures who "benefit" from the higher PPI values.
So what would give me the best Result (example Samsung s6 (1440 x 2560 @ ~577PPI)?:
a) Create a Document with 1440x2560 px @ 577PPI and save it that way?
b) Create a Document with 1440x2560 px @ 72 PPI then change the PPI to 577 so i get 11540 x 20515 px @ 577ppi and save it in 1440 x 2560 @ 577 PPI
c) ??
Thanks in advance!

Great design resource

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