Hi Fred,
I thought this little honey pot had much of the information you required, but it might pre-date the enamel sign!
If you google it, there are some references to Phillips Fine Teas. There's particularly a 1913 photo of Wrexham High Street, with 'a branch of Phillips tea merchants and grocers', suggesting it covered a significant geographiocal area, which sounds like a candidate, but no reference to where their head office was.
It's a sign I've always fancied a good example of, but she has one heck of a chin on her!