BUR #144 is pending approval.
create implication phone_over_face -> covered_face
create implication covering_face -> covered_face
These tags both imply that a person's face is covered in the image.
Covering face not being aliased because it's a deliberate action. A covered face may not inherently be intentionally covered.
There's some other tags such as censored face, covering own face, hands on own face, hand on another's face- but I'm not too acquainted with how things at cosbooru are to be handled just yet. Personally, I think covering_own_face would be better to imply, and to either alias or deprecate covering_face due to the ambiguity. On the other hand, how often does one come across another person covering the other's face?