Can i split a microUSB to plug into the wall and computer

In theory yes, they Sell usb Y cables, no need to make one, They use to include them with usb hard drives in the early days of XP when one usb port would not power the enclosure due to the usb 1.1 power specification, so they added another usb pigtail to use power from the second usb port. I still have one of them.

You could use a y cable even if it does not have the correct end for your phone, just use a usb gender changer adapter.