How to implement a phone number change when choosing a city on Bitrix?

Question

PHP

Hello!
I'm trying to implement a change of context on the choice of the city on Bitrix.
Without connecting to any geo-base, because the number of cities is known.
Moscow and Peter.
When you enter the site, a window pops up, there is a RADIO BUTTON And the Select button Choose
Peter at the bottom of the page, the phone number changes.
I created an infoblock with the name of the city and the PHONE property
. I use bitrix.news.list
Here is my code without popup.

<div class="news-list">
<?foreach($arResult["ITEMS"] as $arItem):?>
    <?if($arParams["DISPLAY_NAME"]!="N" && $arItem["NAME"]):?>
      <?if(!$arParams["HIDE_LINK_WHEN_NO_DETAIL"] || ($arItem["DETAIL_TEXT"] && $arResult["USER_HAVE_ACCESS"])):?>
<form name ="" method ="post">
<input type="radio" name="r"><b><?echo $arItem["NAME"]?></b><br />
      <?endif;?>
    <?endif;?>
<?endforeach;?>
<input type = "submit" value = "Выбрать">
  </form>
</div>
</div>
            <?if (isset($_POST['r'])):?>
        <?foreach($arItem["DISPLAY_PROPERTIES"] as $pid=>$arProperty):?>
               <div id="telephone"> <?=$arProperty["DISPLAY_VALUE"];?></div><br />
        <?endforeach;?>
<?endif?>
</div>
</div>

Accordingly, the substitution of the number does not work (

I don’t even know what to do. It’s very necessary that it works automatically if cities are suddenly added or phones change.
Help, please.

Answer 1

Write the currently selected city ID to the cookie. Yes, and the phone can also be entered there and then removed from the cookies. If there are no cookies, then display the phone by default