[solved]order-opc "Phone" disabled by default - why?

[j.kaspar]

Hi, I use one page checkout in 1.6.1.13. In delivery address (order without registration), there are two fields for phone number - phone and phone_mobile. The "phone" is hidden by default. The DIV looks like this:

<div class="form-group is_customer_param" style="display: none;">
  <label for="phone">Telefon <sup>**</sup></label>
  <input type="text" class="text form-control validate" name="phone" id="phone" data-validate="isPhoneNumber" value="">
</div>

I struggle to find out, where the style="display: none;" comes from. It is not in template files (order-opc.tpl / order-opc-advanced.tpl...), nor the scipts (order-opc.js...). I believe it has to be some script, that adds it dynamically. I need to have the DIV visible by default. Can anyone help, please?

Edit: Just want to add, that I use a default-bootstrap template.

Edited April 4, 2019 by j.kaspar (see edit history)

[j.kaspar]

It turns out, that the div is being hidden, when the class=form-group is_customer_param. It looks like this

else if (isGuest)
		{
			$('.is_customer_param').hide(); 
.....

code in order-opc.js does this.