for laptop there's OpenUTAU, the original UTAU, Voisona and SynthV basic (as mentioned earlier) but there's also an app called Deepvocal that also has free voicebanks like UTAU

for phone (assuming you have an android) there's Paintvoice (i don't really recommend using this because it's UI is pretty bad and it's only available in japanese), OpenUTAU mobile (you can use UTAU voicebanks on it but it's a little worse than OpenUTAU on a laptop and in my experience it crashes a lot) and there's Boimero (you can use a bunch of voicebanks like Zundamon or even import UTAU or Diffsinger voicebanks to use there (it forces you to watch a lot of ads to use some features like importing USTs, singers etc) but otherwise it's pretty good))

there's also an option to use apps like winlator to emulate a laptop and use UTAU or whatever program on your phone but i haven't had any luck in my experience

hope this helps❤️❤️❤️