customers.phone is formatted like +91-9876543210 or +1-415-555-0123 — a +, the dial code, a dash, then the national number which may itself contain dashes. Some customers have no phone (NULL).
Return: - customer_id - dial_code — the digits between + and the first - (e.g. "91", "1", "44") - national_number — everything after the first dash, with all remaining dashes removed (e.g. "4155550123")
A NULL phone must yield NULL for both parsed columns (don't invent values, don't error). Sort by customer_id.