Legal Question in Business Law in California

Generally not.

Proxy voting by the members of a nonprofit public benefit corporation is permissible except to the extent limited by the bylaws, and with certain limitations imposed by law as to prior disclosure of subject matter to be voted upon. See Corporations Code section 5613.

However, if we are speaking of a vote by the BOARD rather than a vote of the membership, the situation is different. Corporations Code section 307 dealing with participation in board meetings of corporations in general does not require physical presence of a director if the director can hear and be heard by all other participants, but there seems to be no provision for participation by proxy or proxy voting,

Without an exhaustive study I cannot be completely certain, but it seems that the duties of a director are nondelegable and therefore each must participate, if at all, in person and not by proxy.