Number only validation

[webiter]

I am trying to get the preg_match '/[^0-9]/' thing below to validate or clear number only entries into a phone field. Am I on the right track as currently I cannot get it to work?

public function validatePhone($phoneVal, $phoneName) {
        if (strlen($phoneVal) <= 0) {
            $this->setError($phoneName, "Phone Number Required");
        } else if (!preg_match('/[^0-9]/', '',$phoneVal)) {
            $this->setError($phoneName, "Valid Phone Number Required");
        }
    } 

<p><label>Phone: <span class="required">Required</span>
          <input type="text" name="phone" class="textfield" value="<?php echo htmlentities($phone); ?>" />
          </label><span class="errors"><?php echo $phoneErr ?></span></p>

Thanks in advance for your oversight.