For anyone reading I was able to resolve this myself using the following code:
<script>
function datePickerFixer() { // fixes readonly issue on mobile
document.getElementById('et_pb_contact_input858_0').readOnly = true;
}
datePickerFixer();
</script>
Just replace “et_pb_contact_input858_0” with the ID of your date picker input field. Boom, no virtual keyboard on mobile.