At the risk of becoming boring, I doubt it was just a phone call.......the authorisation will have been properly issued.
Here's the relevant rule..
(b) In the following unforeseen cases, where an aircraft is grounded at a location other than the main base where no
appropriate certifying staff is available, the maintenance organisation contracted to provide maintenance support
may issue a one-off certification authorisation:
1. to one of its employees holding type qualifications on aircraft of similar technology, construction and systems; or
2. to any person with not less than five years maintenance experience and holding a valid ICAO aircraft maintenance
licence rated for the aircraft type requiring certification provided there is no organisation appropriately
approved under this Part at that location and the contracted organisation obtains and holds on file evidence of
the experience and the licence of that person.
All such cases must be reported to the competent authority within seven days of the issuance of such certification
authorisation.
The approved maintenance organisation issuing the one-off certification authorisation shall ensure that
any such maintenance that could affect flight safety is re-checked.