Is reactive attachment disorder just a phase that will go away eventually?

No. Reactive attachment disorder (rad) is one of the more severe childhood mental health diagnoses which almost always requires intensive professional intervention. One of the reasons for this is that children with rad fundamentally have difficulty establishing close relationships with caregivers, which is an essential requirement for both affect and behavioral regulation.
No. There is no quick fix for treating reactive attachment disorder. It takes a great deal of effort, patience, love and time to mend broken relationship and distrust between a child and parent (caregiver).