My activity shows on my watch but not my phone. It stopped showing in my phone when I got a new phone, however it has been quite a few months and still nothing. How do i get it back in my phone?

Also

First force restart the Watch 

i.e. press and hold both the side button and Digital Crown for at least 10 seconds, then release both buttons when you see the Apple logo. 

 Then, although it may seem irrelevant, while it is restarting Force Restart the paired iphone   Force restart iPhone – Apple Support (UK) 

You may also want to make sure the software on the watch and iphone  are both up to date to the same level. Updates are in pairs. 

Update your iPhone or iPad - Apple Support

Update your Apple Watch - Apple Support 

Test it for a while. If it is still misbehaving you may have to unpair and pair again

Iphone Settings, [your name], iCloud, (show all) is Health turned on?

I would check if you are signed into your Apple ID on your watch. To do this, go to the settings app on your watch and check that your name shows up at the top. If not, you need to sign in.

It sounds like you have not paired it properly. Is there a little red phone icon at top centre of the watch face?

Unfortunately unpairing or erasing and setting up again may lose the data.