This is probably a stupid question but how safe is it to have the MagSafe charger close to an iMac screen? Can the magnets have a negative effect on the iPhone screen?
Not a stupid question because it was an issue with colour CRT screens in which (a) magnetic fields could deflect the elecron beams and distort the image and (b) there was a delicate steel shadow mask or aperture grilles just behind the screen which a strong magnet could potentially damage - or, just as bad, magnetise. (Holding a magnet in front of a CRT screen and seeing the effect of a magnetic field on electron beams was good, clean fun but - pro tip - use a B&W screen that doesn't have a shadow mask).
AFAIK, though, there's nothing in a modern LCD screen that can be damaged by a magnetic field - and remember that the pre-2012 iMacs used strong magnets to hold the screen in place back in the good old days before Apple discovered the Kragle...