Hello and welcome, here goes, I’ll come back to your first question at the end.
Rough date of manufacture probably 1890s upto around WW1, assuming the body is four corner bent, which it looks to be.
Yes, the body skins on most were extremely thin- often no thicker than 1/16 of an inch.
The fire resistant material was commonly sand, sawdust and alum crystals, although some lesser makes ended up with anything including the sweepings of the factory floor! Some used plaster of Paris.
Yes, sorry to say it was an average joe at the bottom end of the market.
Regarding the Phillips & Son being the same as the Birmingham maker, my initial thought was probably not, but then saw the decal on your safe has “manufactured for” at the top of the crest, but the name below it looks to have been erased.
Perhaps it was made by Phillips & Son of B’ham, and the Manchester refers to the company for whom it was made? I’m sure someone will know either way, hope this helps.
