When resizing a frame you can control whether:
Horizontal alignment is a paragraph attribute which can be altered via the Text context toolbar. Vertical alignment of text within a frame is a frame attribute. The latter is good for aligning text centrally with adjacent graphics.
With the text frame selected, do one of the following:
The frame text will reflow within the newly sized frame; the font size will remain unchanged.
With the text frame selected, drag the object's scale handle (this extends from the bottom-right corner of the frame).
The frame text will resize in proportion to the new frame's dimensions.