Posted: 16/04/2017 at 18:19
Philadelphus best pruned after flowering. Cut a third or so of the older stems right back to base. More will grow. Do the same next year and the year after and you'll bring it back to a smaller size.
If you cut all the branches back to a height to suit you now, you'll end up with what one forum member referred to as 'the shaving brush' effect. Lots of people do that and don't seem to mind a shapeless shrub as long as it flowers. So do whichever suits you.