Trying to get viewModel in phtml

I’m trying to get viewModel in two areas inside phtml. I’m getting an error (Fatal Error: 'Uncaught Error: Call to a member function getviewmodelText() on null).
My code for ViewModel is :
Phtml file :

$viewModel = $block->getViewModel();
     $heelDetail = $viewModel->getviewmodelText($item);

Default.xml :

    <referenceContainer name="content">
                 <block name="size">
                    <arguments> 
                        <argument name="viewModel" xsi:type="object">MycodeSalesViewModelSize</argument> 
                    </arguments> 
                </block>
            </referenceContainer>

Block Code :

    namespace MycodeSalesViewModel; 
    
    use MagentoFrameworkViewElementBlockArgumentInterface; 
    
    class Size implements ArgumentInterface 
    {
          
        public function getviewmodelText($item)
        {
             return $item; // add a dollar sign here
    
        }
     }