Not with the default music player, but FLAC is pointless on a phone like the XS
It's DAC, and the DAC for any phone out there for that matter, aren't up to par for FLAC files, and they just drain more battery power while taking up more space. Stick to V2 VBR MP3s for phones, good balance between SQ, battery and space overall
Quite frankly, if anyone says that FLAC makes a major difference on a mobile phone setup, where the DAC is built for power saving rather than full on performance (same goes for the amp section), I'd like to challenge them to a blind ABX test
Reserve FLACs for desktops with a proper DAC + AMP + cans setup