该问题通常是由于POST请求发送不正确或未正确处理请求的响应导致的。需要检查代码中POST请求的正确性，并确保在发送请求后正确解析响应。 以下是一个使用Apache HttpClient发送POST请求并处理响应的示例代码：

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.util.EntityUtils;

public class CiscoVoIPPhoneCGI {

    private static final String CGI_URL = "http://example.com/cgi-bin/phone.cgi";
    
    public static void main(String[] args) {
        try {
            
            HttpClient client = new DefaultHttpClient();
            HttpPost post = new HttpPost(CGI_URL);
            
            // 添加POST请求参数
            List parameters = new ArrayList<>();
            parameters.add(new BasicNameValuePair("phone_number", "1234567890"));
            parameters.add(new BasicNameValuePair("message", "Hello World!"));
            post.setEntity(new UrlEncodedFormEntity(parameters));
            
            // 执行POST请求
            HttpResponse response = client.execute(post);
            HttpEntity entity = response.getEntity();
            
            // 处理响应
            if (entity != null) {
                String responseString = EntityUtils.toString(entity);
                // 根据响应内容进行适当的处理
            }
            
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}