I made a document in calc of the residents of my community. I need to update it. When I tried to change a phone number and deleted the contents of that cell, the new digits were a totally different font. Each time I had to go up to the font and size and fix them before adding the new number. How can I make it so the new cell is the same as all the old ones?
Yes, this mishmash of fonts can be super annoying.
The solution is to change the font in the style settings, rather than by formatting the individual cells. Go to Format → Styles → Styles and formatting (or just press F11), then right click on the Default style and press Modify…, select the Font tab and pick the font you want.
There may still be cells that retain their individual formatting, so to clear that, select the cells (CTRL + A), then go Format → Clear direct formatting (or just CTRL + M).
Also, you may find that if you paste phone numbers from somewhere else (e.g. a web page or Writer document) that those may come with their own formatting. To paste without formatting, click Edit → Paste special (or CTRL + SHIFT + V) and make sure Formats is not ticked.