The obstruction is the toilets internal trap or the closet bend.
You can rent a toilet auger or remove the toilet tank, bowl and fix it that way.

To touch on what snoonyb posted.
Sounds as if you have blockage in the internal trap of the commode.

Found a commode cutaway to show the traps design. The trap is within the green outline. You can use a snake to clear blockage. Then when attempting to flush a large amount of solids. Using a snake may not work depending on what the solids were.

At times it is better to just shut off the water supply.

Drain the tank (flush) and then remove as much water as possible. A wet dry vac is good for removing most of the water.

Unbolt the commode from the floor and carefully turn it upside down in the bath tub.

Pour a large amount of water down through the drain to "back flush" it.

Having the commode out does a couple of things.

Commode upside down allows you to work from both ends of the drain/trap and makes it easier to see a blockage if one exist.

You can pour water directly into the floor drain to check the flow. If you find blockage in the drain. having the commode out makes it much easier to snake the line.

And last it gives you a chance to replace the wax gasket which must be done whenever a commode is removed from the floor.

Both previous posts are good information and to that I will add tips that might make removing the toilet unnessary. If you have a commode topper cabinet or shelf,burn it or only store large items in it. Things get knocked off into the toilet and flushed resulting in these problems. If you have a toddler,try to only alow toys in the bathtub that are too large to go into toilet trap. Jr will play with Ducky in the toilet where it gets flushed. Many abjects float so remove water in bowl as Hippy suggested before useing a snake(aka closet auger) in hopes the object might fall back down into bowl while snaking. With no water in bowl,I use a small mirror to see Ducky,hair roller and other objects and retrive with a bent coat hanger when a snake will not do the job. This may suprise many but a pencil lodged in the trap will cause a lazy flush while no body waste or paper is present. Add body waste and/or paper and it will do exactly like yours is doing.

After the toilet is unused for several hours, pour a bucket of water into the bowl quickly.
If it flushes normally, the problem is not in the bowl trap or the drain line. If it flushes slowly, the problem is in the bowl trap or the drain line.
Report the results and additional help, if needed, can be posted.