One user, Dylan McKay, reported that from October 2016 to July 2017 his logs contained 'the data of every [mobile] call I've made, including time and duration' and 'data about every text message I've received or sent'.
The discoveries came after some Facebook users tried to delete their profiles over the Cambridge Analytica scandal.
Rather than delete an account entirely, the social media site encourages people to 'deactivate' their profile as this leaves all personal data on its servers.
However, when users request to permanently delete their accounts, the site suggests: 'You may want to download a copy of your info from Facebook.'
It is this data dump which revealed the extent of the data held. User Mat Johnson said he found his deleted Facebook profile data dump contained information on 'every single [mobile] phone call and text I made for about a year'.
Emma Kennedy found Facebook had recorded 'every single phone number in my contacts.
'They had every single social event I went to, a list of all my friends and their birthdays, and a list of every text I've sent'.
A Facebook spokesman said: 'The first time you sign in on your phone to a messaging or social app, it's a widely used practice to begin by uploading your phone contacts.
'Contact uploading is optional. People are expressly asked if they want to give permission to upload their contacts from their phone – it's explained right there in the apps when you get started.
'People can delete previously uploaded information at any time and can find all the information available to them in their account and activity log from our Download Your Information tool.'
The company says an opt-out for uploading contacts is available and users can delete all uploaded contacts by turning off the continuous uploading setting in Facebook's Messenger app.
All previously uploaded contacts are deleted when a user permanently removes their profile. Contacts will also no longer continue to be uploaded.
The findings follow days of allegations that data analytics firm Cambridge Analytica harvested data on millions of Facebook users without permission for political campaigning.
Last week as the backlash grew, the co-founder of messaging service WhatsApp, Brian Acton, suggested it was time for users to 'delete Facebook'.
And a poll of more than 1,000 people by Sky News found 65% said they trusted Facebook less now than a week ago.
Facebook printed apologies from founder Mark Zuckerberg in UK newspapers yesterday.
The full-page advert said: 'We have a responsibility to protect your information. If we can't, we don't deserve it.'
In the advert, Mr Zuckerberg said a quiz developed by a university researcher had 'leaked Facebook data of millions of people in 2014'. He added: 'This was a breach of trust, and I'm sorry we didn't do more at the time. We're now taking steps to make sure this doesn't happen again.'
Mr Zuckerberg has until today to tell MPs if he will give evidence to them about Facebook's links to Cambridge Analytica.