Glenn,
I'm not sure where you got the form from. The middle (=I fear) is φοβέ-ομαι = φοβοῦμαι when contracted.
φοβέω (φέβομαι ‘flee in terror’; Hom. et al.; Wsd 17:9; Jos., Ant. 14, 456), in our lit. only pass. φοβέομαι (Hom.+; OGI 669, 59; SIG 1268 II, 17; pap, LXX, pseudepigr., Philo, Joseph., Just.; Mel., P. 98, 746 al.; Ath. 20, 2; R. 21 p. 75, 1) impf. ἐφοβούμην; 1 fut. φοβηθήσομαι; 1 aor. ἐφοβήθην (Plut., Brut. 1002 [40, 9]; M. Ant. 9, 1, 7; Jer 40:9; Jos., C. Ap. 2, 277; s. B-D-F §79).
Arndt, W., Danker, F. W., & Bauer, W. (2000). A Greek-English lexicon of the New Testament and other early Christian literature (3rd ed.) (1060). Chicago: University of Chicago Press.