It is understandable, but can be improved. "You are considered" is present-tense, but "on last Monday" refers to a past-tense event. Even though it is accurate that he is still 'considered' absent now as well as then. So I would have written: "You were considered absent from work last Monday for not answering work-related calls, and there will be a deduction from your salary." Even better would be to put the time first, then the status, then the result: "Last Monday you were considered absent for not answering work-related calls; there will be a deduction from your salary."