Depends on your jurisdiction. Ripping a dvd or bluray in the first place would be illegal in the states. Any type of format shifting (including say CD to mp3) is illegal in the UK - even if you did buy a drm free WAV, unless the copyright holder explicitly gives you permission to copy it to your phone, or another computer, you're stuck.
https://www.avvo.com/legal-answers/is-it-legal-to-rip-a-dvd-...
Some like to claim DMCA could be used to prosecute someone for bypassing the encryption on a DVD for personal backups but this has, to my knowledge, never been tested in court when an individual defendant was purely using it for personal backups.
There has been a case in favor of DMCA seeking to restrict the release of selling products that allow users to to this: https://www.eff.org/cases/realnetworks-v-dvd-cca-realdvd-cas...
That was an insane call, and it is a pity they didn't appeal as AFAICT.
A similar issue to this was challenged recently with DMCA being used to stop the distribution of the open source youtube-dl tool making the same anti-circumvention claims but in the end this fizzled out as having no merit.
If anyone from Hollywood really wants to test this in court I will happily publish a video of myself ripping one of their DVDs that I purchased for personal use. It would not be a good look for them to to anything about it, and would bet a -lot- that they lose. Still, I would like to see this chilling effect gray zone be put to rest so people are not scared to use their rights.
One of your many rights if you -actually- own a copy of media.
Many sites offer DRM-Free music and books without needing to have a redundant physical copy laying around, but in video media this is extremely rare, and that is a problem.