Yes you can write blog post from your phone. I am not a fan of writing a blog post from the smart phone but you can make it work. While working on your phone, there is not a lot of free tools needed to write a blog post from your phone. What is needed is not a tool, you need a app called WordPress app.
The WordPress app is where you can write your blog post on. You can write your title and you can start writing your post. You can write your just like your write a text or an email. It is harder to write on a phone than a desktop. You can use an easier keyboard for writing but I don’t think of any free tools to help write a blog post. You just need to open up your WordPress app and just start writing. Here’s the link that will take you to the app store for Google play store and the apple store
Google play store: https://play.google.com/store/apps/details?id=org.wordpress.android&hl=en_US&gl=US
Apple store: https://apps.apple.com/us/app/wordpress/id335703880
