My wife's camera has an SD card. She only uses a phone / tablet and both only have micro USB port for charging. I see there are card readers that have a micro USB port, in fact I have one. I use the other USB end to copy photos from my SD card to my computer.

 

When I plug it into the wife's micro USB charger socket on the phone or tablet the devices don't seem to recognize the card, or not that I can see anyway. I have gone into file explorer on the phone, can't see anything. Am I doing something wrong or does the phone / tablet not have this ability? The phone is an Oppo A31

They do make card readers specifically for phones.  I have one that works well.  Finding one that's compatible can be a challenge.  I have a few e'l cheapo card readers, some work with phone & laptop, some don't ... ????

 

If only a few photos, I simply upload via Gdrive.  Depending what using for, and quality I want, if not important, then I'll upload to FB msgr.  Gdrive will upload in full original size/format.

 

More than a few photos, then easier simply to use readers of phone cable.

I've gone through this route, just checking your model of phone it supports OTG so I think the problem may be that your card reader is not OTG compatible. When I had a phone that was Micro USB I bought an OTG hub, from memory around 400 baht, put my non OTG Transcend USB 2.0 card reader into one of the ports and the phone recognised it via the hub. It's easy with my USB C phone now as Transcend have a Type C Card reader that is OTG compatible, no problems.

 

Try one of these cheapies from Lazada 

 

https://www.lazada.co.th/products/sdmicrosdtf-card-reader-to-type-c-micro-usb-usb-lightning-otg-adapter-usb30-i1189966704-s6637970031.html?exlaz=d_1:mm_150050845_51350205_2010350205::12:16450510680!!!!!c!!6637970031!135265863&gclid=CjwKCAjwi8iXBhBeEiwAKbUofT75h6vk6ehfJVbYq4zmvKI2ovqVy_gVw39ISw-IZoQO6x2qFr9V0RoCCosQAvD_BwE

 

 

you need to go into the Oppo settings - Additional settings and turn on OTG connection.

 

By default its off

Just now, croftrobin said:

you need to go into the Oppo settings - Additional settings and turn on OTG connection.

 

By default its off

Oh thats great, I did get a little adapter but would recognize the adapter at all. Will check it out tomorrow. Thanks so much

you need turn it on each time you use it, as it turn itself off after 10 minutes of inactivity.  A damn nuisance!