Many thanks for these two four prompt and helpful replies.
I hadn't seen the probate inventory at all and may well try to get a copy.
I had seen the entry for Joshua Phipps (son of Robert, upholsterer) to become a fishmonger (but not that for Robert son of Robert that you also kindly point me to.)
I can see, for example, this explanation of the guilds:
Membership in a guild could be taken up in one of three ways: by completing a seven year apprenticeship, by patrimony (if one's father was a member of the company), or by redemption (payment of a fee). None of these routes of entry ensured that the member would actually practice the company's trade. Owing to the Custom of London, members of London guilds could practise any trade in the City. Consequently, even though a completed apprenticeship remained the most common route to membership, guilds often included numerous members who did not actually practice the relevant trade. The ratio of members practising the craft to others varied from guild to guild, with the less prestigious guilds such as the Carpenters' Company having a larger number of practicing craft members. Other companies, such as the Grocers', Fishmongers', and Goldsmiths', had many fewer practising members, and, owing to the high cost of admission, became "little more than gentleman's clubs"
Looking at the detail, Joshua was admitted to a seven year apprenticeship to a master, John Towers, when he would have been 12. He married just two months after the seven years were complete, which seems coherent.
By contrast, his older brother, already being entitled to membership of the company of upholsterers by virtue of his father's membership before his birth, was admitted to the more prestigious company of fishmongers by payment of a fine when he, as the older brother, would have been at least 17.
For some reason, I still can't see a christening record for Robert, and the one that I have for the second Joshua is only an 'index record'. The same was true for the record I had for Elizabeth Maria (I already had the date), but Lily's comment on that prompted me to look again and I found another. The records for Elizabeth Maria and for the first Joshua both state:
"I baptised the son/daughter of Robert and Mary Phipps upholsterer in Houndsditch in the Parish of Aldgate and named him/her ..."
And thanks to Lilly for the comment on his apprenticeship. Finding the image of the second baptism record mentioning upholsterer for Elizabeth Maria has convinced me beyond doubt that they must be the same family. I had already seen a record for Robert Phipps taking in apprentice upholsterers so, unless this was just a scam, he must have been one.
Since I know that he was a freeman before the birth of Robert (himself born at least nine months before December 1744) and that an apprenticeship must have lasted seven years, I was going to start looking for apprenticeships starting no later than 1736.
Anyway, all this is remarkably helpful so many thanks. I am still left wondering how he got to be so rich and am therefore more inclined than before to try to get hold of the inventory.
Alan