Can I fit ASUS Phoenix GeForce® GTX 1050 Ti 4GB GDDR5 or at least it's low profile on my DELL OPTIPLEX 9020 ssf CPU?

The manual doesn't list a power limit on the PCIe slot, and it has 2 slots of space, so low profile GTX1050Ti should be OK. Don't worry about the seemingly low PSU rating. The Optiplexes almost always have a 95W CPU limit, and there are almost no expansion slots or drive bays to power in an SFF computer. So CPU and GPU=165W. max.
If you can find a low profile GPU that needs it there is a 315W SFF PSU that has a 4 pin CPU, 8pin MB, and 6 pin PCIe cable. It's basically a 240W PSU with a 75W PCIe cable added =315W.