Yeah if the games are running on DOS you don't need Win98 to boot them. Just open the ISO or the zip files with DOSBox-Pure.
That being said for Win98 you can have an image as large as you want, but in your case on the smartphone you had to use 2GB due to size constraints IIRC. Proper DirectX versions will usually install along the game. And you shouldn't bother to mess with drivers except if you want early Windows games with 3D accelerated graphics running, like Half Life or Quake 3. Check
this tutorial video if you want to go down that route. I got the drivers from
https://www.philscomputerlab.com/drivers-for-voodoo.html
Also, Windows being Windows, using it in a VM like DOSBox, it will always be less stable than the real thing and prone to corruption if you dont tediously shut it down safely everytime. So you should copy your disk image (the .img file in Retroarch/system) and have as many backup version as you want to test things.
I don't plan to stay active on this forum, it's more and more polluted by advertisement and mods censoring with the same "rules" they have in mainstream gaming sites. If DOSBoxPure gives you trouble you should directly go to the Libretro forums. It's a process to be able to post there, as their antibot policy is really tight, but you'd get direct answers from the devs.
https://forums.libretro.com/