If, in fact, Phillip Garrido "became a member" of the Brentwood or Oakley congregations during this time period, as one source alleges, then he would have been subject to one or more internal judicial actions by his congregation's Body of Elders.
That is a huge 'if'.
It is very likely that he had some type of contact and was under the influence of the cult's teaching at that time, but "became a member" suggests baptised. I'm not aware of anything in the news that suggests that he might have been baptised before he got thrown in the slammer. His activities may well have got the attention of the BOE, but "internal judicial actions" available for dealing with non baptised associates were very limited.
It would be very interesting to know when his mother was contacted, studied and was baptised.
Do you have any links to the history of Phillip? A timeline maybe? I did one for Nancy at the time, but never bothered with Phillip. Now I wish I had.