Both these devices will be under the Lumia range of smartphones from the company. Nokia Phi is expected to be the new flagship smartphone. In terms of design this smartphone will draw resemblance to Nokia Lumia 900 and Lumia 800 and will also have typical polycarbonate body (Watch: Design philosophy of Nokia Lumia 900).
Nokia Arrow on the other hand is expected to be another mid-range Windows Phone 8 smartphone from Nokia, which may have a 4-inch or 4.3-inch display. As of now, not many details about this smartphone are available.
On a separate note, it's also being speculated that Nokia also has a smartphone similar to Nokia Arrow codenamed Atlas in works. This smartphone is perhaps the CDMA version of Arrow and is expected to be launched in US later in the year.
Nokia, which was earlier the undisputed leader in the handset market, is now finding it difficult to maintain its lead, especially in the smartphone segment. It is betting big on the Windows Phone-based smartphone to capture lost market share. It had launched an entry level Windows smartphone - Nokia Lumia 610 in India for Rs. 12,999. This smartphone features a 3.7-inch display, 5MP camera, 800MHz processor and 8GB of internal storage. Nokia Lumia 610 is currently running on Windows Phone 7.5, but company has promised an update to Windows Phone 7.8 sometime later this year. However, the Lumia 610 and other Windows Phone 7.5-based phones will not be able to upgrade to Windows Phone 8.