For example DocA has a field Mobile Number of type Phone. This mobile number field is set as a Search Fields in the DocA.
DocA is a Link field in DocB. In the Link field of DocB when try to search records of DocA by entering Mobile Number it does not work.
N.B: When I set field Mobile Number to type Data, it works.
Findings till now: Searchability only works for FieldType [Data and Link]