Number of digits in a phone number

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User Salimatou has sent us the following question:

How do i restrict the number of digits for a telephone number?

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See here for a recommended way of collecting phone numbers:

Length of Numeric Fields

Hi there, We currently have a survey in field and discovered that numeric questions sometime allow 10 digits to be entered, but sometimes only allow nine digits. For example you can input 2,000,000,000 but you cannot enter 3,000,000,000. This is a repeat survey from a few years back and in the last wave we were able to enter 10 digits always and now this time there seems to be this restriction. Is this an intended feature or a bug? Thanks!