Get ContactID by number

It can be implemented in 2 ways:

1) by using $filter expression of the OData protocol. Please feel free to find examples in the article by the link below:  https://academy.bpmonline.com/documents/technic-sdk/7-13/examples-requests-filter-selection

2) by creating a custom configuration service. The article by the link below describes the entire process of implementation: https://academy.bpmonline.com/documents/technic-sdk/7-13/how-create-custom-configuration-service