Can I get custody of my nephew who was put in foster care by his father?

My nephew (age 14) was admitted to a mental facility in May by his father (sole surviving parent). My nephew was diagnosed with PTSD, ODD and ADHD. His father is a recovering alcoholic, and is bio-polar/manic depressive. My nephew was recently released from the mental facility and placed into foster care at the request of his father for a minimum of 6 months. My nephew is upset with the arrangement and has repeatedly asked for my help and the ability to visit me. My parents (his grandparents) and I have tried to contact the social worker who refuses to return our calls and instead calls the father who just calls us irate and tells us not to get involved. Over the past 2 years, his father, has asked us to allow my nephew to move in with us but has since changed his mind since he had him admitted. I believe there is a fear of losing the social security he collects for my nephew.