Yes. Both phases of the programme can be attended on a full-time or part-time basis, with students permitted to change the way they attend the respective courses. Consult the Part-time Student Study Regulation.
If the student works, experience indicates that, although such work does not prevent successful completion of the taught part of the programme, they will find it difficult to complete it within the usual time frame, which means that, probably, the best option is to enrol as a part-time student, at least for the non- taught part of the programme.
In terms of the respective regulations, whenever the supervisor believes that the student’s activity indicates a strong probability that they will be unable to conclude the PhD within the allotted time or will be very late in their submission, the supervisor should propose to the Scientific Council: (i) that the student studies on a part-time basis; or (ii) that they be excluded from the programme.