Try replacing this line:
field.model.updateRow(field.row,'PersonMobilePhone',stringValue,{initiatorId: field._GUID});
with this:
field.model.updateRow(field.row,'PersonMobilePhone',<b>phonevalue</b>,{initiatorId: field._GUID});
Also, I’m assuming that the API name of “PersonMobilePhone” is correct and it’s not “Person_Mobile_Phone__c” or something. Out of curiosity what type of field is PersonPhoneMobile?