I have lost my other phone how can I locate it

We cannot help you directly however you can help yourself. Read below.

To locate it in the Find My [Device] app, you must have activated the Find My app BEFORE the iPhone was lost. Here is some information on that app ➔ If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support.

Note that your lost iPhone must be able to make the connection to the internet via Wi-Fi or cellular connection so that it can mark its location and broadcast it. 

Axel F.

Use an internet browser and log into www.icloud.com/find

Other options and more information in If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support