What should one do if their phone rings while they are performing supererogatory (nafila) prayers at work; should they conclude their prayer and answer the phone?

One should not interrupt a supererogatory (nafila) prayer to answer the phone unless failing to answer would result in harm, such as emergency calls. As for interrupting an obligatory worship without a legitimate shar'i reason, it is impermissible by the consensus of jurists, based on the words of the Almighty: "And do not invalidate your deeds." However, it is permissible to interrupt it for a legitimate reason, such as killing a snake or aiding someone in distress. Regarding work, an employee may set aside time for ablution (wudu) and the obligatory (fard) and regular supererogatory (ratiba) prayers, as long as the employer has not stipulated against performing supererogatory prayers.