It really depends how much of the Enviro pHAT or pHAT BEAT functionality you want to retain, since both of them have stuff on the top that you wouldn't want to cover with another pHAT.
In the pHAT BEAT's case you have the VU meter, and Enviro pHAT has the temperature sensor (which wouldn't give very useful readings if it were sandwiched between two boards) and the colour/light sensor (which wouldn't give any readings.)
You can, for example, add the pHAT BEAT to the top of your Pi, then carefully soldered the 4-5 wires required to run the Enviro pHAT to the bottom.
You could stack them with an 11mm stacking header: https://shop.pimoroni.com/products/2x20-pin-gpio-header-for-raspberry-pi-2-b-a
Or you could break them out and sit them side-by-side using a Black HAT Hack3r: https://shop.pimoroni.com/products/mini-black-hat-hack3r