It was not known whether he was able to find his phone in the end, said the reports, citing unnamed sources.
Mt Fuji, an active volcano and Japan’s highest peak, is covered in snow for most of the year.
Its hiking trails are open from early July to early September, a period when crowds trudge up the steep, rocky slopes through the night to see the sunrise.
People are dissuaded from hiking outside of the summer season because conditions can be treacherous.
The symmetrical 3776m mountain has been immortalised in countless artworks, including Hokusai’s Great Wave. It last erupted around 300 years ago.
In a bid to prevent overcrowding on Mount Fuji, authorities last year brought in an entry fee and a cap on numbers for the most popular Yoshida Trail.
Starting this summer, hikers on any of Mt Fuji’s four main trails will be charged an entry fee of 4000 yen ($47).
-Agence France-Presse