can i delete an app from iphone without deleting it from apple watch?

No you need to have it on the iPhone for it to work, unless it is downloadable as a stand alone app.

You can find stand alone apps from on the app store on your watch.

You can unistall it from your watch yes.

On your iPHone

My Watch>Installed on Apple Watch>tap on the app you wish to remove, then toggle off "Show on Apple Watch"