Replaces a target's primary phone number with a different one and returns the new number. The old number is released. How the replacement is chosen depends on swap_details: give a specific number to swap to that number (it must already be in the company's reserved pool, and the company must have the reserved_pool experiment enabled), give an area code to take an available number from that area code, or omit swap_details to have one chosen automatically from the reserved pool, falling back to the target's office area code.

Rate limit: 1200 per minute.