Perhaps you should guide him toward this discussion board with a view to the fact that "fixing" phimosis
does not involve surgery, least of all circumcision. There would be very few if any "medical conditions" which would render phimosis unable to be treated and in fact, any such condition
should be actively treated (in order at least to prevent further damage).
So that's the
first aspect of the matter. We describe and focus here on the process of simple (albeit not entirely effortless)
stretching of the skin using firm, perhaps uncomfortable and
consistent (persistent, some minutes at a time or more permanent) tension. Not only is this do-able, but I suggest that if you
reside with this fellow, you are in a position to be intimately
involved in such a process.

How "sexy" that may be is - well, that depends, doesn't it?
What is useful about having the foreskin
persistently covering the glans, is that it is essentially more
rugged and indeed, it is very
flexible so that you can do things - such as gently biting or tugging with your teeth - that you
never could with the glans itself, as well as simply squeezing with your lips. You can do some funny things such as blowing it up like a balloon. (You might have heard that this is dangerous as you could blow air into the urethra and bladder.
Actually even that is largely harmless bearing only a slight risk of introducing bacteria, but
in practice that is quite hard to do anyway. And the same applies to a vagina.

)
Other than that, the most obvious thing is to attempt to get your tongue in and under the foreskin to circle his glans.
In
actuality, oral sex (fellatio, that is,) is "not all it's cracked up to be". I shall accept that you made previous partners very pleased with it and in view of common (quite incorrect and frankly perverse in fact) perceptions of the penis as "unclean", there is a substantial component here of a "compliment" when a woman offers to use her mouth to give pleasure in this way (and equally if not more so when the man performs such for her).
Nevertheless there are quite substantial
limitations; it is difficult to keep the teeth from contacting (and they are generally
very unpleasant when they do), saliva is a
poor lubricant having insufficient actual mucous component, the shape of the mouth does not conform well to the penis (unless you actually
can "deep throat" - and that would not be a common skill), the penis is too
large to suck on effectively and it is very tiring to move one's head sufficiently rapidly back and forth to actually result in ejaculation. It is almost always actually necessary to stroke with the hand while simply holding the glans in the mouth. Tell me if this is not so.

All in all, you probably
are doing just fine whatever you are doing (as Jim intimates). I trust the fellow returns this compliment in kind.