Perhaps your Mac isn't able to share content any longer if it hasn't
an update to Mac OS X; or if the iPhone iOS is older. They get to a
point if they're too far apart, they cannot share content anymore.
Because this 'systems information' is lacking in your post, others
may only guess. However, I've four different Apple products, two
iOS Devices on their last upgrade ( cannot go further.) As well as
four other Macs with differing Mac OS X; from 10.5.8 to 10.11.6.
Between settings, even if these iOS devices and Mac OS X ones
should be able to 'see' the other. If your Mac can 'see' iPhone in
the Find My Mac app (or vice-versa) that's one of a few tell-tales.
Can you check your iCloud settings to see if the devices and Mac
are able to sync or share? Sometimes this is not important, but if
you prefer that some do not share (such as mobile bookmarks in
your Mac version Safari; I've seen this, and don't like it) there may
be other settings or things to check.
Certain obsoleted systems or marginal feature ones go wanting at
some point; so if the issues are not 'settings based' the hardware
or system may be out-of-date. Sorry to not be more helpful.
At the time of my reply, there were no other responses here.
Good luck in any event...! 🙂