Hello!
This is default code in oc-content/themes/user-profile.php:
<div class="control-group">
<label class="control-label" for="phoneMobile"><?php _e('Cell phone', 'bender'); ?></label>
<div class="controls">
<?php UserForm::mobile_text(osc_user()); ?>
</div>
</div>
We can check if osc_user() array contains a phone number, if it does we can make field uneditable by changing <?php UserForm::mobile_text(osc_user()); ?> with custom input to avoid core changes.
<div class="control-group">
<label class="control-label" for="phoneMobile"><?php _e('Cell phone', 'bender'); ?></label>
<div class="controls">
<?php if(@osc_user()['s_phone_mobile'] != '') { ?>
<input id="s_phone_mobile" type="text" name="s_phone_mobile" value="<?php echo osc_user()['s_phone_mobile']; ?>" disabled>
<?php } else { ?>
<?php UserForm::mobile_text(osc_user()); ?>
<?php } ?>
</div>
</div>
Regards.