A "telephone bidder" refers to a person who participates in an auction by calling and bidding over the phone instead of being physically present at the auction location. Full definition
[33] Dschungel (Jungle)(1967), a romantic landscape from that used magnified Benday dots from a newspaper in the style of Roy Lichtenstein, sold from the collection of Count Christian Duerckheim to an unidentified telephone bidder for $ 9.2 million at Sotheby's in 2011; [34] by 2015, it sold again for $ 27.1 million. (en.wikipedia.org)
Richard Diebenkorn's 1979 Ocean Park No. 117 also exceeded its high estimate when it went to an unidentified telephone bidder for $ 6.6 million. (artforum.com)
This luminous wall - size painting (261.6 x 158.7 cm) was purchased by anonymous telephone bidder for staggering price of $ 66,245,000, going well above its unofficial estimated price of $ 50 million. (widewalls.ch)