。
I'll call you as soon as I find out.
Literal
Understand [as soon as-次第] [honorific-お]phone do-humbly.
~次第 means 'as soon as' — attached to the verb stem: 分かり次第 (as soon as I know). お電話いたします uses double politeness: the honorific prefix お + the humble verb いたす (humble form of する). This is keigo — business-level politeness.