。
She called me at an absurd hour last night.
Literal
She [topic-は] last-night absurd time [at-に] phoned-came.
とんでもない is a useful Japanese adjective with several flavors: 'outrageous, absurd, unthinkable, ridiculous.' Originally とんでもない as 'no place to fly to' (飛んでもない), the meaning has drifted to 'out of bounds, beyond reason.' Modifies a noun to mean 'an absurd X, an outrageous X' — とんでもない時間 ('an absurd hour'), とんでもない値段 ('a ridiculous price'). The に here marks the time at which the call happened. Note 電話してくる as a compound: 電話する ('to call') + ~てくる ('toward speaker').