Source : Webster's Revised Unabridged Dictionary (1913)

Phenomenal \Phe*nom"e*nal\, a. [Cf. F. ph['e]nom['e]nal.]
   Relating to, or of the nature of, a phenomenon; hence,
   extraordinary; wonderful; as, a phenomenal memory. --
   {Phe*nom"e*nal*ly}, adv.

Source : WordNet®

phenomenally
     adv : to a phenomenal degree; "his reaction was phenomenally
           quick"