As I'm not getting my copy of Phil's book until next month (as a Birthday present!), can anyone shed more light on this comment which I saw in a review, such as which period of time he was talking about?

It's essentially the Flesh + Blood/Avalon time period. As an example Phil had arranged to go on holiday in late 1980 when Roxy had decided to record Jealous Guy as their Lennon tribute, but came back to find that Bryan had got Neil Hubbard in to record a guitar part in his absence. Phil's contribution therefore felt something of an after thought.

Thanks for that. I thought it might be that period, or even the post 2001 period when Roxy had three guitarists on stage sometimes.
With F&B it was clear that Phil was the main man, other than BF playing guitar on the title track. However, with Avalon the dynamic had changed. As a guitarist I'm not alone in not being sure about who plays what in terms of guitar. And of course TTUO (the JG B-side) features Neil Hubbard with no Phil. So I wonder what went on at that time. Just to cover myself no slight against NH meant at all - by all accounts he's a very reasonable individual.
At least on the 2022 tour the guitarist pecking order was very clear.