It depends, but the common sense answer is that you won’t get fired if it is a random occurrence and doesn’t happen often. But the first place you should check is your employee handbook. Your employer will most likely have a clear policy on telephone usage in the workplace and you should make sure you stick to that policy. But when dealing with your employer, always use good judgment and common sense. Sporadic personal calls on an emergency basis that do not interfere with your work product are unlikely to upset your employer whereas frequent personal calls which interrupt your work day and disrupt the work place are likely to be met with more severe disciplinary action. The general rule of thumb to follow is that cellphone or telephone usage for texting or personal calls during the work day will be frowned upon and give your employer the impression that you are not fully engaged and focused on your job.