so i got a new phone and want to deactivate my old phone how do i do that if my phone is not with me

Erase a device

1. Open the Find My app and choose the Devices tab.
2. Select the device you want to remotely erase.
3. Scroll down and choose Erase This Device.
4. Select Erase This [device].

If your missing device is covered by AppleCare+ with Theft and Loss, you shouldn't erase your device. Instead, file a claim for your lost or stolen device.

What happens if you erase a device

When you erase your device, all of your information (including credit, debit, or prepaid cards for Apple Pay) is deleted from the device, and you won't be able to track it using Find My. 

Where is your old phone?

No you cannot.

That suggestion will not work as your old iPhone is dead and can’t be communicated with.