Negotiated low speed on phone's wifi

Hi guys,

Recently i have very weird problem. I pay for 300mbit and wired connections i have it. But weird thing: On laptop i got those 300mbit most of a times but on my phones its like a lottery. For half an hour i got those 250mbit+ but then out of the blue i got 1mbit xD I found on router settings that normally my phone negotiate ~780mbit speed but when that problem happen i got 30/18mbit negotiated. Can somebody tell me why is that? Router is 2-3 meters from me, no walls, i scanned networks nearby and on 5ghz there is few wifi's at channels ~40-50 but my router automaticly switch to free channel ~120.

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Any ideas why my phone negotiate so low speeds?