Hello, RWFarley!

I have thought about a workaround, which in best case works, in middle case does nothing, in worst case erases bookmarks from mobile.
So make a backup of bookmarks first.

1. On PC: enter your login, password and NEW Secret Phrase. It will erase all bookmarks from server; that's why bookmarks from mobile should be back-uped.
2. On mobile, somehow make Sync to be aware of the new Secret Phrase and then click "Sync now". It should merge (I hope; I don't know exact functions of the button, and I cannot test it myself, because I cannot log into Sync on mobile, because mobile has Internet not more than one minute in a month, because...) bookmarks from mobile and computer. In worst case, it will replace bookmarks on mobile with bookmarks from computer (that's why I pledge you to backup mobile bookmarks before starting).