He sent Sharon to that house in Notting Hill a few months back but Sharon backed out and left it alone but now we know Phil was kept hostage at the house - so it must be that Phil knows who Gavin is to Sharon. And possible Sharon's solicitor being her real Auntie.
Whaddya think guys?

all far to convenient for my liking - sorry

Kathy, Phil's ex wife just happens to be married to Gavin, Phil's new wife's, biological father

You forget that this is a soap that we are talikng about .........

Maybe he doesn't read DS.

Who once lived in the square and knew Den.... So it makes sense

I think at this point Phil could have found out, but at the same time it's plausible that he still doesn't know because he could have been blindfolded or unconscious when he was taken into the house and when he got away (escape or otherwise) he was hardly in a good way so he may not have looked around or thought too much on the matter. I mean I can't imagine the first thing you do on leaving somewhere you've been held hostage in that state is to go "oh hey isn't this where my wife's dad is meant to live?"