Can you post a picture or 2? My guess is that something is blocking its light. It probably isn't getting enough sun light required to support blooms. This is a beautiful shrub, but it needs full sun and plenty of space to thrive; and not too wet. I hope this helps.

You say the passion flower "may have" smothered your Philadelphus. If it has grown over it you should cut off all of it that is on your side of the fence and give the Philadelphus another chance. It flowers on the mature wood so if the branches were smothered last year flower buds for this year may not have had chance to form. I certainly wouldn't dig it out until you've given it at least one more year open to more light. They don't mind a little light shade as I discovered when I inherited one under some large mature lime trees but nothing likes swamping. Suggest you put in some bright annuals in front of it for this year.

Another possibility may be pruning at the wrong time of year - if it needs pruning this should be done immediately after flowering - any later and you will damage flower prospects for the following year.

You haven't said how long you've had the shrub - over time, Philadelphus benefits from a fairly severe hard prune, usually in winter whilst dormant (thus sacrificing some of the flowers) where half the stems are taken to the ground, spaced out within the bush, not all in one place.

True - I forgot I did this once and it renovated the old bush well.