From Yamaha Wiki
Phazer is the name of a model of Snowmobile produced by the Yamaha Motor Corporation. Introduced in 1984, it became an immensley popular model for Yamaha and spawned several follow-up models (such as the Phazer II, Phazer Deluxe, Phazer Mountain Lite, Phazer FX, and Phazer GT); its design features were also incorporated into other models (such as later-model Exciter (snowmobile) as well as the Venture Lite).
Of particular note on the Phazer is way in which the headlight is directly connected to the handlebars so that the headlight follows the direction of a turn. This feature was certainly new among Yamaha models when it was introduced in 1984, and Yamaha claims that it and other features 'began a new era in snowmobiling'. The Phazer was always known for its sharp handling, free-revving 485cc fan-cooled engine, solid reliability (most notably on Phazer II), light weight, and most importantly, value. It was not so well known for its ride quality, however, as with many Yamaha's of the day. To this very day the Phazer remains one of the best beginner sleds available. .
Snowmobiles under the original Phazer name appear until 1989; new models such as the Phazer II, Phazer Deluxe, etc., were sold until 2001. For the 2002 model year the Phazer nameplate was axed, where it would take a 5 year absence. Yamaha released a bold new snowmobile under the Phazer name-plate for the 2007 model year.  The snowmobile featured a radical new design which is inspired from the YZ250F motocross bike. The new Phazer is powered by a new 80hp 499cc fuel-injected liquid-cooled 4-stroke twin which makes its peak power at 11,000RPM. The engine is based on Yamaha's highly successful and dependable YZ250F dirt bike engine. With a 487 pound estimated dry weight, it is one of the lightest production 4 strokes.
The 4th generation Phazer is hoping to continue the legacy that was started 23 years ago, using the same principle as the original; provide a light-weight, high-revving, ground-breaking machine that anyone could afford and have fun on, this philosophy was highly successful and sent Yamaha to #1 in the snowmobile market-share world, where it would stay until the early 90's when Polaris toppled them with their "wedge" chassis and powerful three-cylinder engines in such applications as the XLT, XCR and fuel-injected RXL.