The iPhone ringtone is an audible alert that plays when you receive an incoming call or notification on an iPhone. Over the years, Apple has introduced various default ringtones with each new iPhone model and iOS update. However, since my knowledge is based on information up to September 2021, I can describe some of the iconic and commonly known iPhone ringtones up to that time:

1. Marimba: This was one of the earliest and most recognizable default ringtones on the iPhone. It features a bright and pleasant marimba sound, and it became synonymous with iPhones when they were first introduced.

2. Opening: The "Opening" ringtone had a distinctive and uplifting melody, often associated with iOS devices. It was also a popular choice among iPhone users.

3. Reflection: This ringtone had a more calming and mellow sound. It was a gentle and slightly echoey melody.

4. Chimes: Chimes was a soothing ringtone with a set of repeating chime-like notes that sounded relaxing and subtle.

5. Synth: The "Synth" ringtone featured a futuristic and electronic sound, giving it a more modern vibe compared to the traditional melodies.

6. Strum: The "Strum" ringtone mimicked the sound of a guitar strum and had a catchy, folksy feel to it.

7. Xylophone: Similar to the marimba, the "Xylophone" ringtone was bright and cheerful, with a xylophone-like sound.

Keep in mind that Apple may have introduced new ringtones or changed the defaults in more recent iOS updates beyond my knowledge cutoff date. Additionally, users can customize their ringtones by adding their own music or choosing from a selection of other tones available on the device.