noun
international telephone number
A telephone number that includes the country code and can be dialed from abroad.
海外からかけるときは、世界電話番号を入力してください。
When calling from abroad, please enter the international telephone number.
国際電話 refers to an international call or international telephone service, while 世界電話番号 is specifically the number itself.
Compound of 世界 (world) + 電話番号 (telephone number).