Is there a way to write a dynamic regex matching using yup in react?

I am currently learning react and encountered an issue. I have a contact info collection page which may display the country code and phone number based on a boolean variable in the form. I am passing it in the context to the validation schema. My schema looks like:

export const contactValidation = yup.object().shape({
  phoneNumber: yup
    .string()
    .required('this is required')
    .max(10, 'only 10 characters allowed')
    .matches(aSimpleRegex, 'the format is incorrect'),
  
  countryCode: yup.object().required('contact country required'),
});

This is not always the case, because I am controlling the display of countryCode based on a boolean variable in the form. I can access the context by doing something like:

const context = this.options.context as ContactContext;
context.countryCodeEnabled;

I would like to use this and only validate the countryCode field when context.countryCodeEnabled is true. Also when it is true, I want to use a different REGEX in the .matches option of phoneNumber.

The issues I am facing with this:

1. I am unable to define a const inside the yup.object().shape
2. If able to access it somehow, how do I use it to control the validation and change the regex as well?

Thank you so much for your help in advance.