Question: what is the maximum length of phone number
[{'answer': '15 digits', 'provenance': [{'wikipedia_id': '627405', 'title': 'Telephone numbering plan', 'start_paragraph_id': 3, 'start_character': 276, 'end_paragraph_id': 3, 'end_character': 285, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '627405', 'title': 'Telephone numbering plan', 'start_paragraph_id': 3, 'start_character': 0, 'end_paragraph_id': 3, 'end_character': 498, 'bleu_score': 0.923732788176137, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 1917201281138708623}, 'section': 'Section::::Abstract.'}]}]