I've actually run mitmproxy on my phone in a chroot before, somehow (several years ago now). However, I can't remember if it was a rooted phone or not, sorry.

Suffice to say it's perfectly possible, most phones are plenty powerful enough.

[EDIT]: if it's not rooted, I know you can still use it with a large portion of mobile traffic by adding the trusted cert it generates and then setting it up as a network proxy through standard settings changes (ie: no iptables transparent proxy necessary). I believe some apps will detect this.