Moderation update: This thread covers two related but separate scenarios. For leads arriving through Zoho Flow, the recommendation is to contact
support(at)zohoflow(dot)com for help with a custom function. For numbers entered manually in CRM, @Haiku Technical Support
shared a neat approach further down the thread: use the built-in zoho.ai.parsePhoneNumber() Deluge task, which parses a number against a country code and returns the E.164 format directly, attached to a Client Script that runs on field change or on save.