As you mention your father is type 2 diabetic .Now present with ankle swelling which now extend to calf.
Its nothing but cellulitis
In diabetic patient cellulitis is very common due to immunocompromise state.
High blood sugar level favours staphyloccal infection.
This cellulitis may convert in abscess
formation later on if not control.
and surgeon,need antibiotic cover for staph in form of amox,serial usg of affected area to see any abscess formation,if abscess form then drain it in addition most important is strict controll of blood sugar level.