Change Text By Window Width

I am trying to change the button text to “Call Me” when the browser window is 1024 pixels or LESS.
The code below works fine until I add the if wi variable.
Does anybody have any ideas for making this work?

……………………………………………………………………………………………………………………………………………………………….

<button id=”phone” class=”button”><a href=”tel:6144788011″ title=”Call Advanced Systems”>614-478-8011</a></button>

<!— Begin Call Button Script —>
<script>
var changeText = document.getElementById(“phone”);
var wi = document.width;
if(wi <= 1024){
changeText.innerHTML = “Call Me”;
}
</script>
<!— End Call Button Script —>

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