I haven’t noticed any significant change, but no iPhone X is going to hold a charge like it did when the battery was new. The max capacity on my iPhone X battery is currently 88%. I bought it about 14 months ago.
On the one hand the iPhone and watch sync data continuously, so that’s going to have some impact on the iPhone battery. On the other hand, as others have said, the watch cuts down on iPhone usage for some of us... which should help preserve the battery, but YMMV depending how much much your iPhone usage actually drops (if the amount is significant at all) while wearing the watch.
I think it would be unusual to actually notice the impact of the watch on the iPhone battery, so I would examine the individual app battery usage on your iPhone. There could be a third party app that is running amok. I would focus on the ones that have Watch apps installed. And if you haven’t already, give both devices a restart. If your Apple Watch is new, just be patient. There is a lot of data transfer and indexing that happens during the first few days and after some major watchOS updates.