Android - Is there a way to access the phone filesystem from computer, wireless?

According to the mentioned requirements, more powerful tool to use is Sambadroid. SambaDroid is a native port for Android of the popular Samba for Linux. This application allows you to share/manage files on your device easily from any device of your network.

Update: With the Windows Creators Update you may (or not) need to first enable SMB Server/Client functionality.

Pros

• No need to use router even a mobile hotpot works fine
• You can easily set a share from your android device (e.g sd card)
• Ability to set shared folder with read/write permissions

Limitations

• Due to limitations in later editions of Windows trying to explicitly map the network drive can result in a "network not found" error. Ignore it and use Windows explorer method.

• Requires root (needed for CIFS implementation on android). Alternatively if not root, then its better to create a shared folder on windows then access it from android with a suitable file explorer, you can still perform file operations.

Setup involves setting the desired share from the device. See screenshot:

^{Note: NO affiliation with the above aplication}

Switch on your mobile hotspot and allow your PC to connect to the network.

Once done just type [Win]+[R] in your computer, write \\SAMBADROID or go to PC >> Network and you will see a new share, see below:

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The samba share will look like this:

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You can perform various functions like delete, copy etc. See below:

Hope this helps.

This solution works even over a hotspot. Simply enable Portable Hotspot on your mobile device, then connect your laptop to the Hotspot WiFi network.

Tip: If you want to prevent the laptop from using your mobile data, simply switch mobile data off while your hotspot is on. The solution will work even without internet access.

1. Install Cx File Explorer on your Android phone (it's completely free, and has no ads!).
2. If your phone and laptop are not on the same WiFi network, enable Portable Hotspot on your phone and connect your laptop to the hotspot.
3. Open Cx File Explorer (give permission), go to the Network tab and open "Access from PC".
4. Tap on "Start Service". You'll see the full FTP address displayed on your phone.
5. On Windows 10, open File Explorer and enter the full FTP address into the address bar.
6. Press Enter, and you'll see a "device" folder. Open it, and you'll see all the file in your phone. If you have an external SD card, you may see it as another folder besides "device".

The following is optional. If you wish to see this FTP server as a location under "This PC":

1. Open "This PC", right-click a blank space and click on "Add a network location".
2. Click Next, then Choose a custom network location, then Next again.
3. Type in the full FTP address that you see on your phone. Click Next.
4. Leave the option "Log on anonymously" enabled. Click Next.
5. Give your location a name. You can leave it as the IP address or maybe name it after your device.
6. Click Next, then Finish.

The FTP server should open in File Explorer like a normal file system. You can drag and drop files, copy and paste, etc.

For more details and other ways to access the FTP server, see this How-To Geek article.

Summary of attempts, thanks to the other answers and my own tests:

• Using a Samba server on phone (with app Sambadroid for example) looks great, but sadly it requires root for reasons explained in Using SMB server without root access, so it's not an option for me.

• Using a FTP server (for example with cx File Explorer app) works great, but it's a bit slow if you have lots of files (even just getting the list of thousands of remote files via FTP is slow), and any FTP client on computer.

• Use a SFTP server (with SSH/SFTP Server app), and then connect it from any SFTP client on computer (such as WinSCP), or rclone for synchronization (rsync won't work since it requires a rsync binary running on remote if I remember correctly).