<?php
namespace {vendor}{module}BlockAccountDashboard;

use MagentoFrameworkViewElementTemplateContext;

class Updatemobile extends MagentoFrameworkViewElementTemplate
{
    protected $_customersession;

    public function __construct(Context $context, MagentoCustomerModelSession $customerSession)
    {
        $this->_customersession = $customerSession;
        parent::__construct($context);
    }

    public function getCustomerid()
    {
        $customerId = 0;
        if ($this->_customersession->isLoggedIn()) {
            $customerId = $this->_customersession->getCustomer()->getId();
        }
        return $customerId;
    }

    public function getMobilenumber()
    {
        $mobileNumber = 0;
        if ($this->_customersession->isLoggedIn()) {
            $mobileNumber = $this->_customersession->getCustomer()->getMobilenumber();
        }
        return $mobileNumber;
    }
}

<div class="update_mob">
    <div class="update_mob_text">
        <input type="text" value="<?php echo $block->getMobilenumber(); ?>" class="updatemobnumber"/>
        <input type="hidden" value="<?php echo $this->getUrl("mobilelogin/index/updatemobilenumber"); ?>" class="url" />
        <input type="hidden" value="<?php echo $block->getCustomerid();?>" class="userId" />
        <span><?php echo __("You will get all the sms on this number"); ?></span>
    </div>
    <div class="update_mob_btn">
        <input type="button" value="Update Mobile Number" class="updatemobbtn action primary"/>
         <img class="sms-request-load" src="<?php echo $block->getViewFileUrl('images/loader-1.gif'); ?>" alt="Please Wait..." id="updatemobile_img"/>
    </div>
</div>