If your phone has NFC interface, then in theory it should be possible to access contactless java smart cards.

https://github.com/doc-rj/smartcard-reader

https://play.google.com/store/apps/details?id=com.inoapp.car...

Other than that there are java cards in microSD format such as these

https://news.ycombinator.com/item?id=9625862

http://www.cardomatic.de/epages/64510967.sf/en_GB/?ObjectPat...

Then there's also a shaky area of pkcs11 proxies.