Open the tab on Ultimate Guitar, e.g. Zombie by The Cranberries. Right-click the page and choose View Page Source (or press Ctrl/Cmd + U). Select all, copy, and paste it below — then hit Show tab.
Honestly I recommend just using a Desktop PC to add your tabs, then read them on mobile.
Your saved tabs
Your saved tabs live in the Library. Paste a page source above to read a new one.