Sorry here is a better one of the canopy.

there are many suggestions on line for transplanting and/or pruning your frangipani and they also grow easily from cuttings ..it looks like it would be worthwhile to replace as much of the soil and help balance the shallow root ball better and prune to encourage lower branches

Brilliant thankyou oklouise. I have had success with cuttings before but was hoping to leave the tree in this garden, and I am not sure I can straighten the trunk without moving it further out of the garden bed, or having lower branches too close to the pool fence. I was thinking my only option if I want it in that location is to have a leaning base and attempt to prune to make the top look straighter. I haven't been able to find info as to whether you can have an angled lower trunk and get the top to straighten up, but I like your suggestion of using keywords "pruning to encourage lower branches", I'll give that a try.

check on line details for best time for transplanting in your area because with the small root ball it should be OK to lift it up, refresh the soil and rotate the tree for a better angle and you could also attempt some new cutting to replace the older tree if it becomes too straggly and consider some generous underplanting

The lean can be attractive. I’d leave it to fill out more before making a decision. I’m the meantime top up the soil and get it a feed. Cram as many grass type plants (all the one soft) as under planting. Consider one of the Lomandra. Add some mulch and it will look much better.

Wonderful thanks so much to you both. I really appreciate you taking the time to offer suggestions. That has given me lots of ideas. I might let it fill out more and get the soil better, then at a more ideal time of year I can see if it needs rotating or some less intense pruning than what I had found online (lop the whole top off and it will branch more profusely and lower - don't think I'm quite prepared to try that so I'm glad I checked!)