How to require either one of two fields? (Cyclic dependency error)

What (if possible) is the correct way to define that either the email or phone is a string > 1?

    var formModelSchema = yup.object({
        email: yup.string().email().when('phone', {
            is: (phone) => !phone || phone.length === 0,
            then: yup.string().email().required(),
            otherwise: yup.string()
        }),
        phone: yup.string().when('email', {
            is: (email) => !email || email.length === 0,
            then: yup.string().required(),
            otherwise: yup.string()
        })
    });

Uncaught (in promise) Error: Cyclic dependency: "phone"

[GeoffreyHervet]

    var formModelSchema = yup.object({
        email: yup.string().email().when('phone', {
            is: (phone) => !phone || phone.length === 0,
            then: yup.string().email().required(),
            otherwise: yup.string()
        }),
        phone: yup.string().when('email', {
            is: (email) => !email || email.length === 0,
            then: yup.string().required(),
            otherwise: yup.string()
        })
    },
   // This is what you missed
   [ [ 'email', 'phone' ] ]
);

[Qwal]

I had to use yup.object().shape({...}) with @GeoffreyHervet solution to avoid cyclic dependency error.