Pain back of left ankle & under heel to arch. Swollen ankle only. Xray show arthritis. No sign of fracture. No bruise. Color good. Cant bear weight.

Possible . Plantar fascitis though it doesn't effect the back of the heel. Back of heel would be achilles i suggest MRI at this point if nothing is on x-ray.
Insertional achilles. Insertional achilles tendonitis and calcinosis. Use a heel lift in shoes, do not walk bare foot, use any form of mentholate gel ie: biofreeze 2-3 x daily. Possible use of anti-inflammatory if you are cleared by your doctor.