Placeholder fields are not submitted. You can make it readonly or hidden, to get value when submitted.
<input readonly type="text" name="textinput-disabled" id="textinput-disabled" placeholder="Text input" value="<?php echo $info;?>">
I hope this is helps you.
Thank you.

Disabled fields are not submitted. You can make it readonly or hidden, to get value when submitted.
<input readonly type="text" name="textinput-disabled" id="textinput-disabled" placeholder="Text input" value="<?php echo $info;?>">