Who is Eric (Mother Goose) and Linda Lampton from Valis and what is their importance?

Eric is a British rock star, screenwriter, and actor, who usually goes by his stage name, "Mother Goose." He and his actress wife, Linda star in a low-budget science fiction movie, Valis, that captures the essence of what Horselover Fat has experienced since March of 1974. Needing to understand the complex film, Author Philip K. Dick on behalf of Fat and two friends, Kevin and David, contacts Eric through their agents, ostensibly about a film project. Eric responds with the first half of a two-word cypher, which Phil completes. Eric then phones, questions Phil about drug use and criminal record, and invites the foursome to fly as soon as possible to Sonoma, CA, via Oakland. He wants them to see the uncut version of the movie and discuss various things.